In general, wind power generators can be categorized into two types, namely (a) vertical axis wind power generator and (b) horizontal axis wind power generator. In addition to having smaller wind-swept area, a vertical axis wind power generator always poses unbalanced thrust and torque on tower mast during operation while its returning wind blades head against incoming wind. Therefore, problems in association with low wind energy efficiency, high construction cost, excessive vibration and unbalanced torque hence incurring more maintenance cost and additional guy wires for balancing etc. are found in comparison with a horizontal axis wind power generator. Meanwhile, technology development for horizontal axis wind power generator is mature as reliability in operation with better power output efficiency has been recognized. Thus, horizontal axis wind powered generators are engaged in large scale wind farms all over the world.
A modern commercial wind farm is always located distant from cities at remote area where wind energy source is abundant. Voltage of electricity generated has to be stepped up prior to distribution of electrical power through distant transmission grids to energy consuming factories and cities. High costs in initial investment and thereafter maintenance, high loss of energy in transmission and high cost for power distribution are major problems which engineers and scientists are addressing for.
Wind energy output for a wind power generator is functional to wind-swept area of blades, height of nacelle above ground, and wind speed in accordance with Wind Formula. In this regard, wind power generators are mounted on high towers or masts with large rotor span of wind blades. Apart from high initial investment cost, a wind power generator must be installed distant from building due to vibration and noises in operation thereby prohibiting application of wind power generators in residential dwellings.